I currently have limited electronics experience. I am planning to use mains power through relays for climate control, so considering the risk, I would like to check to see if these relays are appropriately connected to receive mains power.

I have two relays. One relay will take 600W (a heater) while the other will have 50W/0.2A (a fan).

The relay module is: https://www.auselectronicsdirect.com.au/assets/files/(ST1080)5V%20Relay%20module.pdf There seems to be a resistor inbuilt into the casing, and according to the packet (but not the PDF) there is inbuilt Back-EMF protection.

My concern is that it may not be protected against inrush, uses screw terminals, and may not be isolated.

Diagram is: enter image description here

Any advice will be appreciated. Once again, I will not run mains power through it until I am sure of it being safe.

  • The pins of the module are labeled "S + -", you have connected them in the right way. They could be very cheap or counterfeit relays, and the contacts could melt. A heater can have some inductance, that could cause sparks between the contacts. The module is not according to the specifications for the mains voltage. When looking at the back side here: openplatform.cc/index.php/home/index/details/apiid/115 the pin of the diode (low voltage) is very close the pin of the screw terminal (mains voltage).
    – Jot
    Sep 11, 2018 at 0:28
  • The relay on that board (on the photo in the datasheet), is only rated at 125V AC, while you seem to be living in a 220V country. Double check the markings on the (blue) relay on your board. Your wiring looks fine. There is indeed a flyback diode on the board, and a transistor to drive the coil in the relay.
    – Gerben
    Sep 11, 2018 at 14:41

1 Answer 1


Yes, your relays are hooked up the right way. I'm using the same modukes to drive a fan 75W and a HPS-Lamp with 400W. As long as you drive the heater with AC voltage, you're in the specs (different than stated in previous comments). But the humidity sensor (a DHT11/22) isn't, as far as I remember its pinout... And could you explain what the Transistor is for (if it is a transistor, I'm curious what you want to achieve with this wiring)?

  • The wiring was more just the best I could get with Fritzring - it didn't have the actual modules I used. The DHT22 is this: auselectronicsdirect.com.au/… (pins are GND, VCC, DATA as shown in the image). The transistor looking thing is actually a three-pin LDR module (could only find a 2-pin one in Friztring so used something else). Link is: auselectronicsdirect.com.au/…
    – Jack Walsh
    Sep 12, 2018 at 23:49
  • Okay, sorry then! I thought of the raw version of the DHT22 which has 4 pins. Didn't look to your picture well enough...
    – Sim Son
    Sep 12, 2018 at 23:54

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